Carrier transmission over power circuits



July 28, 1925. 1,547,242

M, E. STRIEBY CARRIER TRANSMISSION OVER POWER CIRCUITS Filed April 29, 1924 fwn/ A TTORNEY Patented July 28, 1925.

UNITED STATES PATENT vori-Ica MAURICE E. STRIEBY, OF MILLBURN, NEW JERSEY, ASSIGNOR T0 AMERICAN TELE- t PHONE AND TELEGRAPH COMPANY,

A CORPORATION 0F' NEW YORK.

CARRIER TRANSMISSION OVER 4POWER CIRCUITS.

To all whom t may concern.'

. Be it known that I, MAURICE E. STRIEBY, residing at Millburn, in the county of Essex and State of `New Jersey, have invented certain Improvements in Carrier Transmission Over Power Circuits, of which the following is a specification.

This invention relates to the use of power circuits for the transmission of signaling currents, and more particularly to arrange.- ments whereby ,carrier transmission channels may be capacitatively related to the conductors of av power system.

In accordance with the present invention, a carrier channel is conductively connected to the conductors of a power circuitin such a mannerthat the carrier apparatus will be protected from the high voltages impressed upon the power conductors. The conductive connection is .preferably obtained through a ca acity coupling, the condensers forming tlie coupling'being so designed as to offer a very large impedance at the relatively low frequencies employed in power transmission but being mechanically constructed so as to withstand the high voltages of the power conductors. Between the condensers and the carrier apparatus an inductive shunt is connected across the carrier conductors to form a low impedance path for the low frequency currents employed in power transmission so that any current of power frequency passing through the condenser will to the frequency used for carrier transmis-l be by-passed through the low impedance path. Preferably the inductance of the low impedance path and the capacity of the condensers will be so. proportioned with respect sion that these elements will constitute the first section of a high-pass filter included in the carrier circuit to separate the power frequencies from the carrier frequencies.

The invention will now be'more fully understood from the following detailed description thereof when read in connection with the accompanying drawing, the figure of which illustrates an embodiment of the invention.

Referring to Figure l, T, designates a two-phase transformer of the type ordinarily employed in powertransmission, the windings of the transformer being connected in the usual manner to the power conductors to conductors l and 3.

can be connected to any two of the three conductors. In the sketch connection is made l Coupling capacities 7 and 8 are included in the connections.

E These capacities comprise condensers which are so constructed as to withstand the high voltages of the low frequency power transmission currents which are impressed upon the conductors 1, 2 and 3,- and the capacities of these condensers are so propo-rtioned .that they will form elements of a high-pass filter as hereinafter described. In order to withstand the high voltages, the plates of the condensers have a Wide separation, and speclal dielectric materials are einployed in a manner well known in the art. Inorder that the desired capacity may be obtained, it therefore becomes necessary to make the elements of the condensers mechanically quite large as compared with the type of condenser ordinarily employed in signaling circuits. Below the condensers 7 and 8 protectors of a type well known in the art are employed, these protectors comprising fuses 9 and 10 included in the conductors l and 3 and the usual carbon block type of lightning protector l1. The outer terminals of the device 11 are connected to the conductors l and 3 while the third conductor 2 is connected to ground through the third terminal of the device l1 in order to balance the circuit to ground.

A high-pass filter TF is included between the carrier apparatus T and the power conductors as indicated. This filter, which is preferably of the well yknown Campbell y' of the inductance 12 is made verylow -so this should appear-acrossthe terminals of that the shunt path offers a very low impedf frequency ance to the low frequency power currents which ordinarily have afrequency of about 60 cycles. The inductance of the shunt 12 andthe capacities of the condensers 7 and 8 are so proportioned that at the carrier section of the high-pass lter TF.

. Let .us assume that the power currents have a frequency of 60 cycles and that -,the

these elements may form the firsty -and its ope-ration will be the same, so that vno detailed-discussion thereof is necessary.

voltage impressed .uponthe power conduc.

tors is 2700 volts. The condensers 7 and 8, because of the large separation between their plates andthe eiiicient dielectrics employed, will withstand `these high voltages without breaking down and arcing between the plates, and their impedance at the'power frequency will be vso large that only avery small current Vof the power frequency flows through them.- For eXampleLthe normal current flow` of power frequency through these condensers and across the shunt 12 may be in the neighborhood of one-tenth of an ampere.- If the impedance of the coil 12 at 60 cycles Iis 5 ohms, the voltage drop across the terminals of the inductance 12 will only be one-half a volt. Consequently the voltage across the' terminals of the highpass-filter TF will onlypbe one-half of a volt, and thesignaling conductors will consequently not 'be exposed to the high voltages transmitted over the power conductors.

\ Suppose, now, one of the condensers, for

example, the. condenser .8,'breaks down so up in the by-pass through the inductance 12.'- In order to protectthe carrier circuit, the fuses, such as 4 and 6,v are designed to lblow as soon as the'current builds up'to a value materially higher than that normallypermitted to flow through the inductance 12. For example, these fuses may be made to blow as soon as the current reaches a valueof 3 amperes. A current flow of 3 amperes through the inductance (12. will be 'equival lent to a voltage drop 'across its terminals of only 15 volts at the 60 cycle frequency, and as this is below the maximum voltage which can be impressed upon the carrier con'ductors at the power frequency,no harm lcan occur in the carrier apparatus.` The inductance 12 should be so designed as to .carry a somewhat larger current 'than that vvat which the fuses 4 and 6 breakdown.

Forexample, iflthe fuses are designed, to blow at 3 amperes,.the inductance 12 might be designed to carry 5 amperes. Even for a current iiow of 5 amperes the voltage drop across the terminals of the inductance 12v would only be 25 volts at the power fre.

quency, and this would bea safe voltage for the inductance 12, the fuses 9 and 10'of the protector will become effectiveand prevent damage to the carrier apparatus. Y

The apparatus for connecting a carrier receiving channel to the power conductors, as indicated at vthegright of the diagram,

will be similar tol that already described,

If desired, the choke coils 13, 14 and 15 may be included in the power conductors between the carrier transmitting terminals and thel generator to prevent the carrier currents pling said carrier apparatus to said power 'conductors comprising condensers so designed mechanically as to withstand high voltages, a high-pass filter for preventing the transmission of power frequencies and harmonics thereof to the carrier apparatus,

the capacity of said condensers at the carrier frequencies being` such thatsaid condensers may constitute elements of said filter.

that it is, in effect, short-circuited, the '60. -cycle power current at once begins to buildthe carrier conductors, a shunt inductance' bridged across said carrier conductors,`said inductance'constituting a low impedance b ypass for the relatively small currents of power frequenciestransmitted through said condensers, a Ahigh-pass filter included in lsaid carrier circuit to prevent the transmission of power frequencies and harmonics' thereof to the carrier apparatus, the .capacity of said condensers at the carrier frequency being such'and the inductance of said bypass at the carrier frequency being such that said elements may constitute a sectionV of said filter.

3. In a systemfor signaling over power conductors, a power source, power conduc-y `torsfo-r transmitting power from said source to a load, carrier apparatus, means for coupling said carrier apparatus to said power conductors comprising condensers Aso de signed mechanically as to withstand high voltages, said condensers being included in power frequencies transmitted through said condensers, a high-pass filter included in sald carrler circuit to prevent the transmlsv sion of power frequencies and vharmonics thereof to the carrier apparatus, the capacity of said condensers at the carrier frequency being such and the inductance of said by` pass at the carrier frequency being such that said elements may constitute a section of said filter, and fuses included in the carrier 15 conductors between said condensers and the power conductors, saidy fuses being so designed as to open-said conductors upon one of the condensers breaking down, before the current builds up in. said by-pass to produce a greater voltage drop acrossl its terminals than that which the carrier apparatus is designed to withstand. c

4. In a system for signaling over power conductors, a power source, power conduc` tors for transmitting power-from said source to a load, carrier apparatus, means for coupling said carrier apparatus to said power conductors` comprising condensers so designed mechanically as to withstand high power voltages, said condensers beingincluded in the carrier conductors, a shunt inductance bridged across said carrier conductors, said inductance constituting a low ,impedance by-pass for the relatively small currents of power frequencies transmitted through said condensers, a high-pass `filter 4included in said carrier circuit to prevent the transmission of power frequencies and harmonics thereof to the carrier apparatus, the capacity of said condensers at the carrier frequency being such and the inductan'ce of said by-pass at the carrier frequency being such that said elements may constitute a section of said filter, fuses included in the carrier conductors between said condensers andv the power conductors, said fuses being so designed as toopen said conductors, upon one of the condensers breaking down, before the current builds up in said by-pass to produce a greater voltage drop across its terminals than that which the carrier apparatus is designed to withstand, and fuses-included in the carrier conductors between said bypass and the succeeding section of the highpass filter designed to blow4 if the voltage drop. across said by-pass should become greater than the maximum voltage which it is desired to impress across the terminals of the carrier apparatus.

5. In combination, a power transmission line, a high frequency wave translating system, and a broad band filter, said filter com-J prising a group of impedance elements ada ted to withstand the normal voltage of sai power line and a second group. of impedance elements adapted to withstand the lower voltages of signal transmission'.

6. In combination, a power transmission line, a high frequency wave translating system, and a broad band filter, said filter comprising a plurality of impedance elements and being terminated at on`e end in series elements adapted to withstand the normal voltage of saidpower line, the others of said elements being adapted to withstand the lower voltages of signal transmission.

7. In combination, a power transmission line, a high frequency wave translating system, and a broad band filter, said filter comprising a plurality of sections each including series and shunt impedance elements, and being terminated at one end in a series termination, said series termination Yincluding a condenser adapted to withstand high voltage and the others of said impedance elements being adapted to withstand the lower voltages of signal transmission.

8. In combination, a power transmission line, a high frequency wave translating system, and a broad band lilter, said filter comprising a group of impedance elements including series elements adapted to with- -stand high voltages, a second group of eleed to withstand the. normal voltage of said power line, and a second network connected thereto comprising impedance elements adaptedto withstand the lower voltages of said high frequency source, the elements of said networks being arranged to cooperate with each other to constitute a broad band filter.

10. A broad band filter comprising impedance elements adapted to the low voltages of speech transmission, and terminal' impedance elements adapted to withstand the normal voltages of power transmission.

11. A broad band filter comprising impedance elements adapted tothe low voltages of speech transmission, and terminal condensers adapted to withstand the voltages of high voltage power transmission and including voltage operated protective. devices.

' 12. A broad band filter comprising a plurality of sectionseach including series and shunt impedance elements, and being terminated at one end in a series termination, said series termination including ya condenser adaptedto Withstandhigh voltage age operated piotective device, said. protecand the others of said impedance elements tive device` being vconnected vbetween .said l0.'

being adapted to withstand lower voltages. groups' and being adapted to protect the ele- 13. A broad band filter comprising a ments of said second group. group-of impedance elements including se- In testimony whereof, I have signed my ries elements adapted to withstand highv lname to this speciiication-this 26th day of K voltagesP a second group of elements adaptp-i'il 1924. ed to withstand lower/voltages, and a voltt MAURICE E. STRIEBY. 

